A variety of battery powered portable devices, such as mobile phones, notebook computers and the like, have become popular. Each portable device may employ a plurality of rechargeable battery cells. The plurality of rechargeable battery cells may be connected in series or in parallel so as to form a rechargeable battery pack for storing electrical energy. Rechargeable batteries include a variety of types, such as nickel-cadmium (NiCd) batteries, nickel-metal hydride (NiMH) batteries, lithium-ion batteries, lithium-ion polymer batteries, lithium-air batteries, lithium iron phosphate batteries and the like.
Different types of rechargeable battery packs may employ different charging methods to charge from a depleted state to a full charged state using a power source such as an ac/dc adapter or a universal serial bus (USB) port. In order to have a reliable rechargeable battery pack and a long cycle life, the rechargeable battery pack should operate within a safe operation region to which the rechargeable battery pack is specified. Monitoring the remaining capacity of a rechargeable battery pack is an effective way to keep the rechargeable battery pack operating within the safe operation region. More particularly, an accurate estimate of the remaining capacity of the rechargeable battery pack is important to battery pack users to know the amount of energy left in the battery pack and how much more time the battery powered portable device can be used before the battery pack needs recharging. This is commonly referred to as a battery pack's State of Charge (SOC).
The capacity of a rechargeable battery pack can be calculated based upon the electrical charge flowing into the rechargeable battery pack and the electrical current flowing out of the rechargeable battery pack. The electrical charge may be monitored by a battery fuel gauge apparatus. In accordance with the operation principle of battery fuel gauges, battery fuel gauges may be further divided into three categories, namely a current integration based fuel gauge, a voltage measurement based fuel gauge and an internal impedance measurement based fuel gauge.
A current integration based fuel gauge is based upon an integral of charge and discharge currents of a rechargeable battery pack. More particularly, the battery fuel gauge apparatus detects the electrical charge by means of a sensing device such as a shunt resistor, a Hall Effect transducer, a giant magnetoresistance (GMR) sensor and the like. Furthermore, an analog-to-digital converter (ADC) may convert the analog signal detected by the battery fuel gauge into a digital signal and feed the digital signal to a microprocessor in which a variety of rechargeable battery fuel gauge algorithms may be employed to calculate the state of charge (SOC) of the rechargeable battery pack.
Corresponding numerals and symbols in the different figures generally refer to corresponding parts unless otherwise indicated. The figures are drawn to clearly illustrate the relevant aspects of the various embodiments and are not necessarily drawn to scale.